Conventionally, an element of an anode short-circuit structure shown in FIG. 1 is used as a high power GTO having a low on-state voltage. The reference numeral 1 designates an n type base region comprising an n type silicon substrate. There is produced a p type base region 2 on the n type base region 1. The reference numeral 3 designates p type emitter regions which are produced on the surface region of the n type base region 1. The numeral 4 designates n type emitter regions produced at the surface region of the p type base region 2. The reference numeral 5 designates an anode electrode provided in ohmic contact with the p type emitter region 3. The numeral 6 designates a gate electrode provided in ohmic contact with the p type base region 2. The numeral 7 designates a cathode electrode provided in ohmic contact with the n type emitter region 4. Herein, the anode electrode 5 short-circuits the n type base region 1 and the p type emitter region 3.
In GTOs having such an anode short-circuited structure, the remaining carriers inside the n type base region 1 are extracted through the anode short-circuited portion in turn-off operation, thereby making it unnecessary to shorten the carrier life time of the n type base region 1. As a result, it is possible to realize a low on-state voltage in such an anode short-circited structure GTO relative to the usual GTOs.
In high voltage resistivity GTOs, however, it is necessary to design the n type base region 1 to have a large thickness in view of blocking voltage, and consequently, it is required to shorten the carrier life time even in the anode short-circuited structure. This is because, if the carrier life time of the n type base region 1 is too long, the tail current during the gate turn-off operation becomes long, resulting in an increased turn-off loss and an increased minimum turn off time. These make high frequency operation of the GTO difficult.
Another prior art is disclosed in the U.S. Pat. No. 3,303,360. The semiconductor switch of this patent adopts an anode short-circuited structure aiming at improving the turn-off characteristic thereof.
Another prior art is disclosed in Japanese Laid-Open patent specification No. 58-148086. The thyristor of this laid-open patent specification has an anode short-circuited structure in which a short-circuited emitter with provided directly below the n type emitter. This structure improves the turn-off characteristic without increasing the on-state voltage V.sub.TM.